Post on 15-Oct-2020
transcript
Felix Aharonian Dublin Institute for Advanced Studies, DublinMax-Planck Institut fuer Kernphysik, Heidelberg
Florianopolis, Brazil, March 2016
Short Course on High Energy Astrophysics
Exploring the Nonthermal Universe with High Energy Gamma Rays
Lecture 1: Introduction
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High Energy Astrophysics?
High Energy Astrophysics as a part of more general interdisciplinary area called Astroparticle Physics
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Astro-Particle Physics
modern interdisciplinary research field at the interface of astronomy, physics and cosmology
HE Astrophysics X-, gamma-ray astronomies, cosmic rays neutrino (but also also R,O, UV, …) Relativistic black holes, gravitational waves Astrophysics HE Physics/ “non-accelerator particle physics” Cosmology Early Universe, Dark Matter, Dark Energy
both experiment/observations and theory
ü traditionally is treated as a top priority research activity within the Astronomy/Astrophysics Community ü is strongly supported by the Particle Physics Community for different objective and subjective reasons:
subjective - it is not clear what can be done with accelerators after LHC; in general, APP projects are dynamical and cost-effective; can be realized by small groups on quite short timescales, …
objective - (huge) discovery potential in fundamental (particle) physics (“particle physics without accelerators”)
Golden Age of Astroparticle Physics
Major Objectives of Astroparticle Physics
No 1: Universe - its content (“what is the Universe made of”), history/evolution; how (why) it was created? formation of large-scale structures, magnetic and radiation fields,…
good concepts/ideas - Big Bang, inflation, … established facts: existence of Dark Matter (DM) and Dark Energy (DE), fluctuations of MBR
combined efforts of astronomers and (particle) physicists - to clarify missing “details” - e.g. nature of DM and origin of DE, or reason(s) of asymmetric creation of the Universe
HE astrophysicists are “high-flyers” (as well) at first glance HE astrophysics community has more modest objectives; e.g. for them the study of astrophysics and physics of black holes is not “too boring” and they can discuss over and over “minor” issues like “which particles - e or p ? - produce γ-rays in Supernova Remnants” but, in fact, HE astrophysicists also are “high-flyers” with a (the) major scientific objectives - study the “Nonthermal Universe”. For example they try to understand the origin of Gamma-Ray Bursts - “mini Big Bangs” with a very attractive features (advantage) compared to Big Bang - gamma-ray astronomers detect such explosions every day! These enormous events with energy release 1051erg (or more) over seconds contain also huge cosmological information, e.g. about First Stars
High Energy Astrophysics
a (the) major objective: study of nonthermal phenomena in most energetic and violent forms in the Universe many research topics are related, in one way or another, to exploration of Nature’s perfectly designed machines:
Extreme Particle Accelerators
Knee
Ankle
T. Gaisser
SNRs ?
up to 1015-16 (knee) - Galactic most likely sources: Supernova Remnants SNRs: Emax ~ vshock Z x B x Rshock “standard” DSA theory: Ep,max ~ 1014 eV solution? amplification of B-field by CRs 1016 eV to 1018 eV: a few special sources? Reacceleration? above 1018 eV (ankle) - Extragalactic 1020 eV particles? : two options “top-down” (non- acceleration) origin or Extreme Accelerators
Cosmic Rays from up to 1020 eV
Particles in CRs with energy 1020 eV
the very fact of existence of such particles implies existence of extragalactic extreme accelerators…
the “Hillas condition” - l > RL - a necessary but not sufficient condition…
(i) maximum acceleration rate allowed by classical electrodynamics t-1=ηqBc or c/RL with η ~ 1 and ~ (v/c)2 in shock acceleration scenarios
(ii) B-field cannot be arbitrarily increased - Synch. and curvature radiation losses become a limiting factor, unless … perfect linear accelerators!
only few options survive from the original Hillas (“l-B”) plot: >109 Mo BH magnetospheres, small and large-scale AGN jets, GRBs
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High Energy Astrophysics
addresses an impressively broad range of topics related to the high energy processes in the Universe, including acceleration, propagation and radiation of relativistic particles on all astronomical scales: from compact objects like (neutron-stars and black holes) large-scale cosmological structures (galaxy clusters)
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basic areas
Research Areas of High Energy Astrophysics ü X-ray astronomy ü gamma-ray astronomy ü neutrino astronomy ü Cosmic Rays
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High Energy Astrophysics - in the context of studies of high energy nonthermal processes in UniverseAstroparticle Physics - (1) as one of the cosmic messengers (together with cosmic rays, neutrinos, gravitational waves) (2) in the context of indirect search of Dark Matter, (3) fundamental physics (challenging basic laws) Relativistic Astrophysics - the parents of gamma-rays – relativistic electrons, protons, nuclei are related, in one way or another, to particle acceleration close to relativistic objects: black holes, neutron stars/pulsars, SN explosions … In many cases gamma-ray sources associate with relativistic outflows (pulsar winds and BH jets)
Gamma-Ray Astronomy
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this course after general introduction of the field, the major nonthermal high energy phenomena in different astrophysical environments related to electromagnetic messengers* - X-rays and gamma-rays will be described with emphasis on Very High Energy** domain. The lectures will cover several major topics, in particular § Origin of Galactic and Extragalactic Cosmic Rays § Physics and Astrophysics of Relativistic Outflows § Observational Cosmology *) Cosmic Rays and Neutrinos will be covered in separate lecture blocks **) low and high energy gamma-rays will be covered my separate lectures
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Gamma-Ray Astronomy
provides crucial window in the cosmic E-M spectrum for exploration of non-thermal phenomena in the Universe
in their most energetic, extreme and violent forms
‘the last window’ in the spectrum of cosmic E-M radiation …
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the last E-M window ... 15+ decades: LE or MeV : 0.1 -100 MeV (0.1 -10 + 10 -100) HE or GeV : 0.1 -100 GeV (0.1 -10 + 10 -100 ) VHE or TeV : 0.1 -100 TeV (0.1 -10 + 10 -100) UHE or PeV : 0.1 -100 PeV (only hadronic )
EHE or EeV : 0.1 -100 EeV (unavoidable because of GZK) the window is opened in MeV, GeV, and TeV bands: LE,HE domain of space-based astronomy VHE, .... domain of ground-based astronomy potentially ‘Ground-based γ-ray astronomy’ can cover five decades
(from 10 GeV to 1 PeV) , but presently it implies ‘TeV γ-ray astronomy’
low bound - nuclear gamma-rays, upper bound - highest energy cosmic rays
1MeV=106 eV, 1GeV=109 eV, 1TeV=1012 eV, 1PeV=1015 eV 1EeV=1018 eV 15
10-8 10-6 10-4 10-2 100 102 104 106
γ-rays x-rays ultraviolet infrared mm radio
wavelengths in microns (µm)
γ-rays: photons with wavelengths less than 10-6 µm
gamma-rays are detected from 105 eV to 1014 eV
10-20
106 eV
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a non-thermal astrophysical object seen over 20 energy decades νFν
(W)
1028
1030
1027
Frequency ν (Hz) 1010 1020 1030 1015 1025
1029
1026
1031
radio
visible X rays
soft hard gamma rays
from space
from ground
Crab Nebula
300 GeV 10 GeV 100 TeV 10 TeV
Crab Nebula
100 TeV 10 TeV
from ground
gamma rays from space
X rays soft
hard
gamma-rays R, mm, IR, O, UV,X 17
The Crab Pulsar and Nebula System NASA/CXC/SAO
Palomar Obs.:
2MASS/UMass/IPAC-‐ Caltech/NASA/NSF:
NRAO/AUI/NSF: 18
F. A. et al. Nature 2012
Crab Nebula: powered by rotational energy of the pulsar transported through a cold ultrarelativistic wind
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ü are effectively produced in both electromagnetic and hadronic interactions
ü penetrate (relatively) freely throughout intergalactic and galactic magnetic and photon-fields
ü are effectively detected by space-based and ground-based detectors
gamma-rays – unique carriers of information about high energy processes in the Universe
why gamma-‐rays?
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high energy cosmic gamma-rays
a few general remarks …
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extreme physical conditions generally the phenomena relevant to HEA generally proceed under extreme physical conditions in environments characterized with Ø huge gravitational, magnetic and electric fields, Ø very dense background radiation, Ø relativistic bulk motions (black-hole jets and pulsar winds)
Ø shock waves, highly excited (turbulent) media, etc.
any coherent description and interpretation of phenomena related to high energy cosmic gamma-rays requires knowledge and deep understanding of many disciplines of experimental and theoretical physics, including nuclear and particle physics, quantum and classical electrodynamics, special and general relativity, plasma physics, (magneto) hydrodynamics, etc.
and (of course) Astronomy&Astrophysics 22
Extreme Accelerators
machines where acceleration proceeds with efficiency close to 100% (i) fraction of available energy converted to nonthermal particles in PWNe and perhaps also in SNRs and AGN can be as large as 50 % (ii) maximum energy achieved by individual particles
acceleration rate close to the maximum (theoretically) possible rate sometimes efficiency can even “exceed” 100% ? (due to relativistic and non-linear effects)
radiation and absorption processes
any interpretation of an astronomical observation requires ü unambiguous identification of radiation mechanisms and ü good knowledge of radiation and absorption processes
gamma-ray production and absorption processes: several but well studied
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interactions with matter E-M: VHE bremsstrahlung: e N(e) => e’ γ N (e) * pair production γ N(e) => e+e- N (e) * e+e- annihilation e+e- => γ γ (511 keV line) Strong/week: pp (Α) => π, K, Λ, … ** π, K, Λ => γ, ν, e, µ µ => ν also in the low energy region Nuclear: p A => A* => A’ γ, n
n p => D γ (2.2 MeV line)
Eγ ~ 1/2Ee
Eγ ~ 1/10Ep
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interactions with radiation and B-fields
Radiation field VHE
E-M: inverse Compton: e γ (B) => e’ γ ** γγ pair production γ γ (B) => e+e-‐ **
Strong/week p γ => π, K, Λ, … * π, K, Λ => γ, ν, e, µ µ => ν Α γ => Α* => Α’ γ * B-field synchrotron e (p) B => γ *
pair production γ B => e+e- *
Eγ ~BEe2; hνmax ~ α-1 mc2
Eγ ~ ε(Ee/mc2)2 (T) to ~Ee (KN)
Eγ~ 1/10Ep
Eγ~ 1/1000A Ep
** - very important! 26
gamma-rays produced in interactions of electrons and protons/nuclei often are called leptonic and hadronic interactions but it is more appropriate to call them as E-M (electromagnetic) and S (strong) examples: (i) synchrotron radiation of protons - pure electromagnetic process interaction of hadrons without production of neutrinos (ii) photon-photon annihilation => µ+µ- => neutronos, antineutrinos production of neutrinos by photons as parent particles E-M are calculated with high accuracy and confirmed experimentally S are well studied experimentally and explained theoretically
leptonic or hadronic?
often several processes proceed together => cascades in matter, radiation and B-fields
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